1. Field of the Invention
The present invention relates generally to communication systems and, more particularly, to providing an improved method for controlling roaming in wireless communication systems.
2. Description of Related Art
Global System for Mobile communication (GSM) is one of the most widely used wireless access systems in today's fast growing communication infrastructure. As is well known, main components of a GSM network include a Mobile Station (MS or “mobile”), at least one Base Transceiver Station (BTS), a Base Station Controller (BSC), a Mobile Switching Center (MSC), a Home Location Register (HLR), and a Visitor Location Register (VLR). The MS typically consists of Mobile Equipment (ME) along with a Subscriber Identity Module (SIM). The BTS is physical equipment, such as a radio tower, that enables a radio interface to communicate with a MS. A BTS may serve more than one MS. The BSC manages radio resources, including a BTS, and may be connected to several BTSs. The BSC and BTS components, in combination, are generally referred to as a Base Station System (BSS). The MSC performs a switching function for the network, as well as registration, authentication, location updating, handovers, and call routing, among other functions. The HLR is a database used to store and manage subscriber information for mobile subscribers belonging to a specific network provider. The HLR also stores the current location of each MS. The VLR is a database that contains a profile of subscribers registered on the associated MSC. The VLR also contains information regarding a geographical location of MS's current location.
A GSM network is made up of a hierarchy of geographic areas: cells, location areas (LAs), MSC areas, and a public land mobile network (PLMN) area. A cell corresponds to an area served by one BTS and each cell is assigned by a cell global identity (CGI), which is broadcasted by the BTS. The CGI is made up of a Mobile Country Code (MCC), a Mobile Network Code (MNC), a Location Area Code (LAC), and a Cell Identity (CI). A location area is a cluster of cells served by one or more BSCs, which are themselves controlled by a single MSC. The location area is identified by its Location Area Identity (LAI), which is also broadcasted by a BTS. The LAI is made up of a MCC, a MNC, and a LAC. The MSC area is a region of a network controlled by a single MSC, and typically consists of one or more location area. A PLMN area is an area in which communication services are provided by one network operator (i.e., service provider). Individual PLMNs are identified by their MCC and MNC, where the MNC specifies a home PLMN (HPLMN) of a MS (i.e., subscriber).
When a mobile powers on, the mobile camps onto a cell in which it is currently located and listens for a CGI broadcasted by the BTS of the cell. The mobile then selects a network service provider based only on a MNC and a MCC in the CGI and stores a LAI broadcasted by the BTS. Once the mobile selects a network service provider, the mobile attempts to register with the network by performing a location update procedure.
FIG. 1 illustrates a conventional location update procedure. Mobile 102 initiates a location update procedure by sending a “Location Updating” message to MSC/VLR 108 in visited network 112, via BTS 104 and BSC 106. The “Location Updating” message contains a LAI and an International Mobile Subscriber Identity (IMSI) which consists of a MCC, a MNC, and a Mobile Subscriber Identification Number (MSIN). The MSC/VLR receives the message and determines whether the mobile is allowed to roam on its network. This is accomplished by comparing the MCC and the MNC in the message with current roaming agreements with the mobile's home network operator.
If the mobile is allowed to roam on its network, MSC/VLR 108 sends an “UpdateLocation” message to HLR 110 in the mobile's home network 114. The “UpdateLocation” message contains only the IMSI and a VLR address of MSC/VLR 108. Upon receiving the “UpdateLocation” message, HLR 110 stores the VLR address and responds to the “UpdateLocation” message with an “Insert Subscriber data” message. The “Insert Subscriber data” message transfers data pertaining to the mobile (i.e., subscriber) from HLR 110 to MSC/VLR 108. MSC/VLR 108 acknowledges the receipt of the subscriber data to HLR 110 and the HLR in turn acknowledges the completion of the location updating procedure to MSC/VLR 108. MSC/VLR 108 then sends a “Location Updating Accept” message to the mobile.
In the conventional location update procedure, roaming is determined based only on a MCC and a MNC. This causes problems in geographical areas in which competing network service providers have overlapping coverage. In an area where there is coverage from a home network operator and a competitor, a mobile recognizes both networks' MCC and MNC. However, if the home network operator's signal level and/or quality is lower than that of the competitor's, the mobile selects the competitor's network and may remain camped thereon for some time. This causes the home network operator to incur roaming charges on behalf of the subscriber, thus resulting in a loss of revenue. The home network operator could restrict roaming with the competitor's network. However, this causes roaming to be restricted wherever the competitor has coverage, including areas where the home network operator does not have coverage and wants to roam on the competitor's network.
As a solution, National Roaming Restriction has been implemented. In National Roaming Restriction, a MSC contains information of all the location areas it serves. For each location area, the MSC includes a table of networks (indicated by their MCC MNC) allowed to roam in that location area. FIG. 2 illustrates an implementation of National Roaming Restriction. As shown, mobile 202 initiates location update by sending a “Location Updating” message to MSC/VLR 208. The “Location Updating” message contains an IMSI and a LAI. The MSC/VLR 208 receives the message and determines whether the mobile is allowed to roam (i.e., whether to continue registration of the mobile) on its network based on the LAI. If the mobile is allowed to roam on its network, the MSC/VLR 208 sends an “UpdateLocation” message to HLR 210. If the mobile is not allowed to roam on its network, the MSC/VLR sends a “Location Updating Reject” message to the mobile. In National Roaming Restriction, in areas where there is coverage from a home network operator and a competitor, the competitor's MSC restricts the mobile from roaming in those location areas. Conversely, the home network operator restricts roaming of the competitor's subscribers in certain location areas.
Even though National Roaming Restriction controls roaming, a network service provider must rely on other service providers (i.e., competitors) to provision roaming restrictions correctly. A home network service provider does not have control over roaming of its subscribers. Further, a home network service provider has to depend on a competitor to troubleshoot its subscriber's problem.
In view of forgoing, there is a need for a better solution for controlling roaming.